Pipe forming mandrel with multiple sleeve inner tube

Abstract

An extruder and mandrel assembly is used in a plastic pipe forming apparatus. The mandrel itself is formed from a pair of elongated tubes comprising an inner tube and an outer tube separated from the inner tube by a plastic flow path through the mandrel. The inner tube is formed by a pair of sleeves comprising an inner sleeve and an outer sleeve which is held within the mandrel by the inner sleeve. The inner sleeve is secured at its upstream end to the spider of the extruder head and the outer sleeve is secured by a releasable interlock to the inner sleeve with the releasable interlock being accessible from the downstream end of the mandrel. Therefore, the mandrel does not have to be released from the spider of the extruder head in order to remove the outer sleeve of the inner tube of the mandrel.

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. An extruder and mandrel assembly for use in a plastic pipe forming apparatus, said mandrel comprising elongated inner and outer tubes which define a plastic flow path therebetween for plastic material received from said extruder, said inner tube comprising an inner holding sleeve releasably secured in said assembly by first securing means and an outer sleeve releasably secured on said inner sleeve by second securing means, said inner tube having an upstream end adjacent and a downstream end away from said extruder, said first securing means being provided at said upstream end of said inner tube hidden by said outer sleeve when said outer sleeve is on said inner sleeve, said second securing means being provided and accessible at said downstream end of said inner tube for releasing and removing said outer sleeve from said inner sleeve whereby when the outer sleeve is removed said first securing means becomes accessible for releasing said inner sleeve from said assembly also from said downstream end of said inner tube. 
     
     
       2. The assembly of claim 1 wherein said outer sleeve of said inner tube is made from a plurality of sleeve segments. 
     
     
       3. The assembly of claim 2 wherein each of said sleeve segments is releasably secured to said inner sleeve.